Contact lenses are often exposed to one or more microorganisms during wear, storage and handling. They can provide surfaces onto which the microorganisms can adhere and then proliferate to form a colony. Microbial adherence to and colonization of contact lenses may enable microorganisms to proliferate and to be retained at the ocular surface for prolonged periods and thereby may cause infection or other deleterious effects on the ocular health of the eye in which the lens is used. Therefore, it is desirous to make various efforts to minimize and/or eliminate the potential for microorganism adhesion to and colonization of contact lenses.
Many attempts have been made to develop antimicrobial medical devices. Two approaches have been proposed. One approach is to incorporate antimicrobial compounds into a polymeric composition for molding a contact lens. For example, Chalkley et al. in Am. J. Ophthalmology 1966, 61:866-869, disclosed that germicidal agents were incorporated into contact lenses. U.S. Pat. No. 4,472,327 discloses that antimicrobial agents may be added to the monomer before polymerization and locked into the polymeric structure of the lens. U.S. Pat. Nos. 5,358,688 and 5,536,861 disclose that contact lenses having antimicrobial properties may be made from quaternary ammonium group containing organosilicon polymers. European patent application EP0604369 discloses that deposit-resistant contact lenses can be prepared from hydrophilic copolymers that are based on 2-hydroxyethyl methacrylate and comonomers containing a quaternary ammonium moiety. Another example is an ocular lens material, disclosed in European patent application EP0947856A2, which comprises a quaternary phosphonium group-containing polymer. A further example is U.S. Pat. No. 5,515,117 which discloses contact lenses and contact lens cases made from materials which comprise polymeric materials and effective antimicrobial components. There are some disadvantages associated with this approach for making antimicrobial contact lenses. First, polymeric compositions having antimicrobial properties may not possess all properties desired for contact lenses, especially extended-wear contact lenses, which hinders their practice uses. Second, antimicrobial compounds may exhibit greatly diminished activity since they may not in contact with microorganisms adhered to the surface of contact lens.
The other approach for making antimicrobial medical devices is to form antimicrobial coatings, containing leachable or covalently attached antimicrobial agents, on medical devices. Antimicrobial coatings containing leachable antimicrobial agents may not be able to provide antimicrobial activity over the period of time when used in the area of the human body. In contrast, antimicrobial coating containing covalently bound antimicrobial agents can provide antimicrobial activity over a relatively longer period of time. However, antimicrobial compounds in such coatings may exhibit greatly diminished activity when comparing the activity of the unbound corresponding antimicrobial compounds in solution, unless assisted by hydrolytic breakdown of either the bound antimicrobial compounds or the coating itself.
Currently, a wide variety of antimicrobial agents have been proposed to be used as coatings for contact lenses (see, for example, U.S. Pat. No. 5,328,954,). Prior known antimicrobial coatings include antibiotics, lactoferrin, metal chelating agents, substituted and unsubstituted polyhydric phenols, amino phenols, alcohols, acid and amine derivatives, and quaternary ammonium group-containing compounds. However, such antimicrobial coatings have disadvantages and are unsatisfactory. The overuse of antibiotics can lead to proliferation of antibiotic-resistant microorganisms. Other coatings may not have broad spectrum antimicrobial activity, may produce ocular toxicity or allergic reactions, or may adversely affect lens properties required for ensuring corneal health and for providing the patient with good vision and comfort.
Therefore, there is a need for antimicrobial coatings that can provide high bactericidal efficacy and broad spectrum antimicrobial activity coupled with low cytotoxicity. There is also a need for new contact lenses having antimicrobial coatings, which have high bactericidal efficacy, a broad spectrum of antimicrobial activities, and minimal adverse effects on the wearer's ocular health and comfort. Such contact lenses may have increased safety as extended-wear contact lenses which could provide comfort, convenience, and safety.
One object of the invention is to provide an antimicrobial coating which has a high antimicrobial efficacy coupled with low cytotoxicity.
Another object of the invention is to provide a medical device having an antimicrobial coating that has a high antimicrobial efficacy coupled with low cytotoxicity.
A further object of the invention is to provide a cost-effective and efficient process for forming an antimicrobial coating on a medical device.